1. Field of the Invention
This invention relates in general to a composition for the oxidation dyeing of keratin fibers, in particular human keratin fibers such as hair. More particularly, it relates to pyridine derivatives made by a novel process, which derivatives are used in such composition.
2. Reported Developments
The preferred compound of the present invention, 2,6-dihydroxy-3,4-dimethylpyridine, is known and has been reported by H. Rogerson and J. F. Thorpe, J. Chem. Soc., (1905) 87, 1685 and J. P. Wibaut and E. C. Kooyman, Rec. Trav. Chim. (1944), 63, 231. Years later, the compound and its use in hair-dyeing composition was reported in U.S. Pat. Nos. 4,838,893, 4,900,325 and 5,769,903. The above-quoted patents do not appear to describe the synthesis of 2,6-dihydroxy-3,4-diakylpyridine which, by the literature references, appears to be economically unattractive.
Compounds of substituted 2,6-dihydroxy-3,4-dialkylpyridine are prepared by the following synthetic method shown in Scheme A: 
wherein
R1 is H, C1-C4 alkyl or aryl;
R2 is H, C1-C4 alkyl or aryl;
R3 is methyl, ethyl, t-butyl;
R3 is H, CN, CONH2;
M is an alkali metal, preferably Na or K;
R is methyl, ethyl or tert-butyl; and
Alcohol is methanol, ethanol, isopropanol, propanol, butanols or pentanols.
The preferred compound produced by the method of the present invention is 2,6-dihydroxy-3,4-dimethylpyridine is shown in Scheme B: 